We're sitting in a shooting gallery, with hundreds of thousands of these things whizzing around in the inner solar system. So it's just a matter of time.

We have the capability - physically, technically - to protect the Earth from asteroid impacts. We are now able to very slightly and subtly reshape the solar system in order to enhance human survival.

All of the thrusting is in the inner solar system, then it coasts.

It was a shooting gallery.

Society needs hundreds of hundreds of thousands of Chen Guangbiaos.

But the question is, do I agree with it when it's 1-in-100, when it's 1-in-50, if it's 1-in-20. That is a policy question. At what probability do you begin to spend hundreds of millions or billions of dollars in order to do something?